ABSTRACT: STUDY OBJECTIVES:To estimate the prevalence of obstructive sleep apnea (OSA) in children with Down syndrome. METHODS:Two authors independently searched databases, namely PubMed, MEDLINE, EMBASE, and the Cochrane Review database. The keywords used were "Down syndrome," "Trisomy 21," "OSA," "sleep apnea syndromes," "polysomnography" and "polygraphy." The prevalence of OSA based on apnea-hypopnea index (AHI) greater than 1, 1.5, 2, 5, and 10 event/h was estimated using a random-effects model. Subgroup analyses were conducted for children in different countries, sample size, study year, and risk of bias. Finally, the prevalence of OSA was compared between two types of sleep studies (polysomnography versus polygraphy). RESULTS:A total of 18 studies (1,200 children) were included (mean age: 7.7 years; 56% boys; mean sample size: 67 patients). Five studies had low risk of bias, and nine and four studies had moderate and high risk of bias, respectively. The OSA was evaluated through polygraphy in 2 studies, and polysomnography in 16 studies. For children who underwent polysomnography, the prevalences of OSA based on AHI > 1, 1.5, 2, 5, and 10 events/h were 69%, 76%, 75%, 50%, and 34%, respectively. Subgroup analyses revealed no significant difference among all subgroups. Meta-regression showed that AHI > 5 events/h was inversely correlated with age (P < .001). Moreover, the prevalence of OSA based on AHI > 1.5 events/h was lower in polygraphy compared with polysomnography (59% versus 76%, P = .037). CONCLUSIONS:OSA is highly prevalent in children with Down syndrome. Prevalence of moderate to severe OSA is higher in younger age.